1. Field of the Invention
The present invention relates to a marking line detection system that detects marking lines on the road surface around a vehicle.
2. Description of Related Art
Japanese Patent Application Publication No. 2012-022574 (JP 2012-022574 A) discloses a technology that detects the point groups of white-line candidate points from the white-line detection area on each of the right and left sides of a vehicle and, based on the detected point groups, calculates virtual white-line approximate lines on the right and left sides of the vehicle and determines parallelism between the two virtual white-line approximate lines. If it is determined that the parallelism is low, the technology calculates the approximation error of each of the two virtual white-line approximate lines, determines one of the virtual white-line approximate lines with the lower approximation error as a correct virtual white-line approximate line, and determines the other as an incorrectly recognized virtual white-line approximate line. After that, the technology offsets the virtual white-line approximate line on the correctly determined side to the incorrectly recognized side, compares the virtual white-line approximate line, which has been offset, with the incorrectly recognized virtual white-line approximate line and, then, corrects the position of the incorrectly recognized virtual white-line approximate line.
The technology according to Japanese Patent Application Publication No. 2012-022574 (JP 2012-022574 A) has the following problem. For example, assume that the main driving road and a branching road, which branches to the left and leads to an exit, are mixed on a highway. In such a case, if the approximation error of the virtual white-line approximate line on the left side of the vehicle is larger than the approximation error, of the virtual white-line approximate line on the right side, it is determined that the virtual white-line approximate line on the left side is incorrectly recognized. Therefore, the position of the virtual white-line approximate line on the left side is corrected based on the position of the virtual white-line approximate line on the right side that is determined as correct. This means that, even if the white line of a branching road is detected, this technology can detect the white line (marking line) of the main driving road without being affected by the white line of the branching road. However, if the white line on the right side of the vehicle is a broken line or is obscure due to a scrape, the approximation error of the virtual white-line approximate line on the right side is sometimes larger than the approximation error of the virtual white-line approximate line on the left side. In this case, the technology according to the Japanese Patent Application Publication No. 2012-022574 (JP 2012-022574 A) corrects the position of the virtual white-line approximate line on the right side based on the position of the virtual white-line approximate line on the left side that is the white line of the branching road, sometimes with the result that the white line (marking line) of the main driving road cannot be detected correctly.